Date of Award


Level of Access

Open-Access Thesis

Degree Name

Master of Science (MS)


Marine Science


Bruce J. Barber

Second Committee Member

Paul D. Rawson

Third Committee Member

Steve R. Fegley


The Mytilus edulis species complex includes three smooth-shelled blue mussels, M. edulis (Linnaeus 1 75 8), M trossulus (Gould 1 850), and M galloprovincialis (Lamarck 18 19). When any two of theses species occur sympatrically, hybridization and backcrossing of hybrid and parental genotypes is evident. Despite introgression of genes between taxa their genetic integrity is maintained. To test the hypothesis that a temporal variation in species-specific spawning times is the mechanism limiting hybridization and maintaining genetic integrity in a M edulis and M. trossulus hybrid zone in eastern Maine, mussels were sampled on monthly to semi-monthly intervals throughout 2000 from a low intertidal site in Cobscook Bay. Four polymerase-chain-reaction-based (PCR) genetic markers were used to differentiate between species. Gamete volume fraction (GVF) and oocyte area measurements indicated that both species are temporally synchronized with respect to gametogenesis and spawning. Thus low frequency of hybridization and preservation of genetic identity is not the result of temporally separated spawning times. Limited hybridization may result from gametic incompatibility, differential environmental adaptation, or selective mortality of hybrids. Preferential collection of M edulis seed for aquaculture in Cobscook Bay is thus not possible on the basis of spawning activity alone.